Trasfit 550 Pieces UV Beads Multi Color Changing UV Reactive Plastic Pony Beads, Glows in the Dark, Fun for Jewelry/Bracelets Making (6-8mm) Changes color immediately when exposed to sunlight, even on cloudy and rainy days, The more UV ray, the darker it will be. When the light go out watch these beads glow 7 Assorted Colors: Rose, Orange, Yellow, Fuchsia, Blue, Indigo, Violet Size: 8mm in diameter, 6mm in high, 3mm hole in the middle; Quantity: approximately 550 pieces Fun for jewelry making, and great for teaching UV awareness! NOTE: They need to be put under the ultraviolet first until they turn into different colors; Then they will glow in the dark. The stronger the ultroviolet, the brighter they will glow in the dark. If they don't put under the ultraviolet first, they will not glow in the dark.